1. Field of the Invention
Exemplary aspects of the present invention relate to a charging brush unit, a charging device, and an image forming apparatus, and more particularly, to a charging brush unit, a charging device, and an image forming apparatus for uniformly charging a latent image carrier.
2. Description of the Related Art
A related-art image forming apparatus, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms a toner image on a recording medium (e.g., a recording sheet) according to image data by electrophotography. For example, a charging device charges a surface of a latent image carrier. An optical writer emits a light beam onto the charged surface of the latent image carrier to form an electrostatic latent image on the latent image carrier according to the image data. A development device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the latent image carrier. The toner image is transferred from the latent image carrier onto a recording sheet via an intermediate transfer belt. A fixing device applies heat and pressure to the recording sheet bearing the toner image to fix the toner image on the recording sheet. Thus, the toner image is formed on the recording sheet.
As the charging device for charging the surface of the latent image carrier, a scorotron charging device is known. The scorotron charging device includes a grid electrode and a wire. The grid electrode has a mesh-like shape and opposes a latent image carrier at a predetermined distance. The wire is stretched so that a circumferential surface thereof opposes the latent image carrier via the grid electrode. When a predetermined bias is applied to the wire, and the grid electrode is supplied with a bias closer to a uniform charging potential of the latent image carrier than the bias applied to the wire, corona discharge occurs between the circumferential surface of the wire and the latent image carrier. Accordingly, the surface of the latent image carrier is uniformly charged with a polarity identical to that of the bias applied to the wire. It is to be noted that in order to generate the corona discharge between the wire and the latent image carrier, a voltage of 5 kV or higher needs to be applied to the wire.
One example of a related art charging device includes a so-called sawtooth discharging electrode instead of a wire. The sawtooth discharging electrode includes a plurality of sharp teeth and opposes a latent image carrier via a mesh-like grid electrode. When the discharging electrode is supplied with a bias, electrical charges are concentrated at the plurality of sharp teeth of the discharging electrode opposing the grid electrode, and thus corona discharge occurs at a lower voltage than the voltage applied in the above scorotron charging device including the wire.
However, when the corona discharge occurs, an electrical current flows only from a top of a tooth of the sawtooth discharging electrode, not from the whole surface of the sawtooth discharging electrode opposing the grid electrode. As a result, the latent image carrier may not be uniformly charged. Further, although the related-art charging device may generate the corona discharge at a decreased voltage compared to the scorotron charging device, nevertheless it still needs a voltage of at least 4 kV or higher.